This invention relates to devices employing Tape Automated Bonding (TAB) technology.
In semiconductor device fabrication, TAB is an alternative to the common practice of wire bonding between semiconductor chip pads and lead frames. The TAB approach seems to be enjoying a resurgence of interest since present and future devices require denser pin-outs and interconnections.
In a typical TAB device, conductive fingers are formed on a flexible insulating material, usually polyimide. The conductive fingers extend from the edges of the polyimide to an area in the center. This center portion is removed so that the fingers extend beyond the edges of the cut-away portion and make direct contact with the pads of a semiconductor chip.
There are at least three significant problems with the present TAB technology. First, insulating material such as polyimide can be difficult to selectively etch. Second, once the center section has been removed, the ends of conductive fingers are unsupported, and, therefore, can be difficult to align with the chip pads. Third, it has generally been difficult with the present technology to bond to an array of chip pads which include pads not located on the periphery of the chip surface.
One recent proposal for bonding to an area array of pads has involved forming via holes through a polyimide layer and then forming bonding balls at the ends of the conductive fingers overlying the holes for bonding the fingers to a semiconductor chip positioned below the layer. (See U.S. Pat. No. 4,814,855 issued to Hodgson, et al.)